The difference is that Battle.net is serviced by the developers and it's not a different application that you need to install. The games (Starcraft 2, World of Warcraft, Diablo 3) are designed to run on it and Battle.net is designed for these games. I admit it's not perfect, but it's way better than Steam. You can even play Starcraft 2 without connecting to the service, you'll just be limited to the campaign.
Valve is also a developer. Steam service is an all-in-one-package service that other developers would like to use too. Its DRM solution removes all kinds of silly restrictions that other DRM methods force. Other DRMs, in addition of being 3rd party softwares, commonly behave like rootkits.
Steam doesn't require internet connection every time you want to play a game either!
Also a note on disc versions, they are just backup data and an activation ticket. I will back-up Skyrim, package it in awesome box and send it over to you. When you receive it, I will gift it to you through Steam. To acquire this gift, you have to use internet and Steam naturally. After accepting the gift, you can ignore the online installation and use the disc I sent. The data will be copied and when you run the game, Steam will check updates and create
a unique executable just for you. This is when you no longer need an internet connection. You can put steam in offline mod from now on and play single player campaign.
Steam retail discs are back-up data discs, nothing more.
Little joys of the past might have been fun.
http://i.dailymail.co.uk/i/pix/2008/11/13/article-1085336-02750816000005DC-924_468x314.jpg (wow queue)
And collecting game boxes can feel good.
But these shouldn't be a reason to pass new Elder Scrolls. I want to hear what problem exactly you experienced with Steam, if you don't mind. Also what is it so bad about it? It was a little problematic at first but it was improved. I consider it an excellent service now.
PS. If you don't mind online installation, I can just gift it to you.
PPS. You can ask me other technical problems you have with Steam, I would like to help you sort them out.